diff --git a/src/Services/PassageService.php b/src/Services/PassageService.php
index 6f98b07..09429be 100644
--- a/src/Services/PassageService.php
+++ b/src/Services/PassageService.php
@@ -22,6 +22,21 @@ public function callService(Request $request, PendingRequest $service, string $u
             $headers = array_merge($headers, ForwardedHeaderResolver::forwardedHeaders($request));
         }
 
+        $contentType = $request->header('Content-Type', '');
+
+        if (count($request->allFiles()) > 0 || str_contains(strtolower($contentType), 'multipart/form-data')) {
+            // The multipart branch below builds a brand new multipart body via
+            // attach(), and Guzzle generates its own random boundary for it and
+            // sets a matching Content-Type header — but only when no Content-Type
+            // header is already present on the request (see Guzzle\Client's
+            // "_conditional" header handling). Forwarding the client's original
+            // Content-Type here (with its own, different boundary) would win over
+            // Guzzle's, so the boundary declared in the header would never match
+            // the one actually used in the body, corrupting every multipart part
+            // for the upstream to parse.
+            unset($headers['Content-Type']);
+        }
+
         $service = $service->withHeaders($headers);
 
         if (in_array($method, ['get', 'head'])) {
@@ -39,8 +54,6 @@ public function callService(Request $request, PendingRequest $service, string $u
             return $this->dispatch($service, $method, $uri);
         }
 
-        $contentType = $request->header('Content-Type', '');
-
         // PHP consumes php://input while populating $_POST/$_FILES for
         // multipart/form-data requests, so getContent() is always empty for
         // them — even when the request has no file fields, only text ones.
diff --git a/tests/Feature/PassageRealServerIntegrationTest.php b/tests/Feature/PassageRealServerIntegrationTest.php
new file mode 100644
index 0000000..ff31017
--- /dev/null
+++ b/tests/Feature/PassageRealServerIntegrationTest.php
@@ -0,0 +1,256 @@
+<?php
+
+use Illuminate\Http\UploadedFile;
+use Morcen\Passage\Facades\Passage;
+use Morcen\Passage\PassageHandler;
+
+/**
+ * Real-HTTP-transport integration lane.
+ *
+ * Every other Feature/Unit test proxies through Illuminate\Support\Facades\Http::fake(),
+ * which never touches Guzzle's real URI resolution, redirects, multipart
+ * encoding, or streaming — exactly where the riskiest bugs live. These tests
+ * instead proxy through a real PHP built-in web server (see
+ * tests/Fixtures/real-server-router.php) so body encoding, header/query
+ * forwarding, streaming, and the allowed-hosts guard are exercised against
+ * an actual socket.
+ */
+class RealServerProcess
+{
+    private static ?self $instance = null;
+
+    /** @var resource|null */
+    private $process = null;
+
+    private ?string $logFile = null;
+
+    private int $port = 0;
+
+    private bool $ready = false;
+
+    public static function instance(): self
+    {
+        return self::$instance ??= new self;
+    }
+
+    public function start(): void
+    {
+        if ($this->process !== null) {
+            return;
+        }
+
+        $this->port = $this->findFreePort();
+
+        if ($this->port === 0) {
+            return;
+        }
+
+        $this->logFile = tempnam(sys_get_temp_dir(), 'passage-real-server-');
+        $router = __DIR__.'/../Fixtures/real-server-router.php';
+
+        $process = @proc_open(
+            [PHP_BINARY, '-S', "127.0.0.1:{$this->port}", $router],
+            [1 => ['file', $this->logFile, 'w'], 2 => ['file', $this->logFile, 'w']],
+            $pipes,
+        );
+
+        if ($process === false) {
+            return;
+        }
+
+        $this->process = $process;
+        $this->ready = $this->waitUntilAcceptingConnections();
+    }
+
+    public function stop(): void
+    {
+        if ($this->process !== null) {
+            proc_terminate($this->process);
+            proc_close($this->process);
+            $this->process = null;
+        }
+
+        if ($this->logFile !== null && file_exists($this->logFile)) {
+            unlink($this->logFile);
+        }
+    }
+
+    public function isReady(): bool
+    {
+        return $this->ready;
+    }
+
+    public function baseUri(): string
+    {
+        return "http://127.0.0.1:{$this->port}/";
+    }
+
+    private function findFreePort(): int
+    {
+        $socket = @stream_socket_server('tcp://127.0.0.1:0', $errno, $errstr);
+
+        if ($socket === false) {
+            return 0;
+        }
+
+        $name = stream_socket_get_name($socket, false);
+        fclose($socket);
+
+        return (int) substr($name, strrpos($name, ':') + 1);
+    }
+
+    private function waitUntilAcceptingConnections(): bool
+    {
+        $deadline = microtime(true) + 5;
+
+        while (microtime(true) < $deadline) {
+            $connection = @fsockopen('127.0.0.1', $this->port, $errno, $errstr, 0.1);
+
+            if ($connection !== false) {
+                fclose($connection);
+
+                return true;
+            }
+
+            usleep(50_000);
+        }
+
+        return false;
+    }
+}
+
+class RealServerEchoHandler extends PassageHandler
+{
+    public function getOptions(): array
+    {
+        return ['base_uri' => RealServerProcess::instance()->baseUri()];
+    }
+}
+
+class RealServerStreamingHandler extends PassageHandler
+{
+    public function getOptions(): array
+    {
+        return [
+            'base_uri' => RealServerProcess::instance()->baseUri(),
+            'passage_streaming' => true,
+        ];
+    }
+}
+
+class RealServerAllowedHostHandler extends PassageHandler
+{
+    public function getOptions(): array
+    {
+        return ['base_uri' => RealServerProcess::instance()->baseUri()];
+    }
+}
+
+class RealServerDisallowedHostHandler extends PassageHandler
+{
+    public function getOptions(): array
+    {
+        return ['base_uri' => 'http://upstream.invalid.test:1/'];
+    }
+}
+
+beforeAll(function () {
+    RealServerProcess::instance()->start();
+});
+
+afterAll(function () {
+    RealServerProcess::instance()->stop();
+});
+
+beforeEach(function () {
+    if (! RealServerProcess::instance()->isReady()) {
+        $this->markTestSkipped('Could not start the PHP built-in server used for real-server integration tests.');
+    }
+});
+
+describe('real HTTP transport', function () {
+    it('forwards a JSON body, custom headers, and query parameters over a real socket', function () {
+        Passage::post('real/json/{path?}', RealServerEchoHandler::class);
+
+        $response = $this->withHeaders(['X-Client-Header' => 'from-client'])
+            ->postJson('/real/json/echo?filter=active', ['name' => 'Ada']);
+
+        $response->assertOk();
+        $payload = $response->json();
+
+        expect($payload['method'])->toBe('POST')
+            ->and($payload['path'])->toBe('/echo')
+            ->and($payload['query'])->toBe(['filter' => 'active'])
+            ->and(json_decode($payload['body'], true))->toBe(['name' => 'Ada'])
+            ->and($payload['headers'])->toHaveKey('X-CLIENT-HEADER', 'from-client');
+    });
+
+    it('forwards a urlencoded form body over a real socket', function () {
+        Passage::post('real/form/{path?}', RealServerEchoHandler::class);
+
+        // PassageService forwards this branch's raw request body verbatim
+        // (see its comment on why it doesn't re-encode $request->post()), so
+        // the raw content must be set explicitly here — Laravel's post()
+        // helper only populates the parsed request/post array, not the raw
+        // body a real client's request would carry.
+        $response = $this->call(
+            'POST',
+            '/real/form/echo',
+            content: http_build_query(['username' => 'ada', 'role' => 'admin']),
+        );
+
+        $response->assertOk();
+        $payload = $response->json();
+
+        expect($payload['post'])->toBe(['username' => 'ada', 'role' => 'admin']);
+    });
+
+    it('forwards a multipart file upload byte-for-byte over a real socket', function () {
+        Passage::post('real/upload/{path?}', RealServerEchoHandler::class);
+
+        $file = UploadedFile::fake()->createWithContent('avatar.txt', str_repeat('a', 1024));
+
+        $response = $this->post('/real/upload/echo', ['label' => 'profile', 'avatar' => $file]);
+
+        $response->assertOk();
+        $payload = $response->json();
+
+        expect($payload['post'])->toBe(['label' => 'profile'])
+            ->and($payload['files'])->toHaveKey('avatar')
+            ->and($payload['files']['avatar']['name'])->toBe('avatar.txt')
+            ->and($payload['files']['avatar']['size'])->toBe(1024);
+    });
+
+    it('streams a chunked upstream response back to the client over a real socket', function () {
+        Passage::get('real/stream/{path?}', RealServerStreamingHandler::class);
+
+        $response = $this->get('/real/stream/stream');
+
+        $response->assertOk();
+        expect($response->streamedContent())
+            ->toBe("chunk-0\nchunk-1\nchunk-2\nchunk-3\nchunk-4\n");
+    });
+
+    it('rejects an upstream host outside allowed_hosts before making a real network call', function () {
+        config()->set('passage.security.enforce_allowed_hosts', true);
+        config()->set('passage.security.allowed_hosts', ['127.0.0.1']);
+
+        Passage::get('real/disallowed/{path?}', RealServerDisallowedHostHandler::class);
+
+        $this->get('/real/disallowed/echo')
+            ->assertForbidden()
+            ->assertJson(['error' => 'Upstream host is not permitted.']);
+    });
+
+    it('allows an upstream host in allowed_hosts over a real socket', function () {
+        config()->set('passage.security.enforce_allowed_hosts', true);
+        config()->set('passage.security.allowed_hosts', ['127.0.0.1']);
+
+        Passage::get('real/allowed/{path?}', RealServerAllowedHostHandler::class);
+
+        $response = $this->get('/real/allowed/echo?ok=1');
+
+        $response->assertOk();
+        expect($response->json('query'))->toBe(['ok' => '1']);
+    });
+});
diff --git a/tests/Fixtures/real-server-router.php b/tests/Fixtures/real-server-router.php
new file mode 100644
index 0000000..db78ca6
--- /dev/null
+++ b/tests/Fixtures/real-server-router.php
@@ -0,0 +1,55 @@
+<?php
+
+/**
+ * Router script for PHP's built-in web server, used by
+ * tests/Feature/PassageRealServerIntegrationTest.php to exercise Passage
+ * against a real HTTP connection instead of Illuminate\Support\Facades\Http::fake().
+ *
+ * `/stream` returns a chunked, flushed body so the streaming code path can be
+ * exercised for real. Every other path echoes back everything PHP itself
+ * parsed from the request (method, path, query, headers, raw body, parsed
+ * POST fields, and uploaded files) as JSON, so the test can assert on what
+ * actually arrived over the wire rather than what Passage intended to send.
+ */
+$uri = parse_url($_SERVER['REQUEST_URI'] ?? '/', PHP_URL_PATH);
+
+if ($uri === '/stream') {
+    header('Content-Type: text/plain');
+
+    for ($i = 0; $i < 5; $i++) {
+        echo "chunk-{$i}\n";
+        if (function_exists('ob_flush')) {
+            @ob_flush();
+        }
+        flush();
+        usleep(10_000);
+    }
+
+    return;
+}
+
+$headers = [];
+
+foreach ($_SERVER as $key => $value) {
+    if (str_starts_with($key, 'HTTP_')) {
+        $headers[str_replace('_', '-', substr($key, 5))] = $value;
+    } elseif (in_array($key, ['CONTENT_TYPE', 'CONTENT_LENGTH'], true) && $value !== '') {
+        $headers[str_replace('_', '-', $key)] = $value;
+    }
+}
+
+$files = array_map(
+    fn (array $file) => ['name' => $file['name'], 'size' => $file['size']],
+    $_FILES
+);
+
+header('Content-Type: application/json');
+echo json_encode([
+    'method' => $_SERVER['REQUEST_METHOD'],
+    'path' => $uri,
+    'query' => $_GET,
+    'headers' => $headers,
+    'body' => file_get_contents('php://input'),
+    'post' => $_POST,
+    'files' => $files,
+]);
diff --git a/tests/Unit/PassageServiceTest.php b/tests/Unit/PassageServiceTest.php
index a28f665..fc8d942 100644
--- a/tests/Unit/PassageServiceTest.php
+++ b/tests/Unit/PassageServiceTest.php
@@ -335,6 +335,33 @@ public function all(?string $key = null): array
             expect($this->service->callService($request, $pending, 'upload'))->toBe($mockResponse);
         });
 
+        it('excludes the client Content-Type header for a multipart request, so Guzzle can set its own boundary', function () {
+            // The attach()-built multipart body below gets a fresh, randomly
+            // generated boundary from Guzzle. Guzzle only sets a matching
+            // Content-Type header for it when none is already present on the
+            // request — forwarding the client's own Content-Type here (with its
+            // own, different boundary) would silently win instead, so the
+            // boundary declared in the header would never match the one the
+            // body actually uses, corrupting every multipart part for the
+            // upstream to parse.
+            $file = UploadedFile::fake()->create('avatar.png', 10, 'image/png');
+            $request = Request::create('/test', 'POST', server: [
+                'CONTENT_TYPE' => 'multipart/form-data; boundary=----ClientBoundary',
+            ]);
+            $request->files->set('avatar', $file);
+
+            $mockResponse = Mockery::mock(Response::class);
+            $pending = Mockery::mock(PendingRequest::class);
+            $pending->shouldReceive('withHeaders')
+                ->once()
+                ->withArgs(fn (array $headers) => ! array_key_exists('Content-Type', $headers))
+                ->andReturn($pending);
+            $pending->shouldReceive('attach')->once()->andReturn($pending);
+            $pending->shouldReceive('post')->once()->with('upload', [])->andReturn($mockResponse);
+
+            expect($this->service->callService($request, $pending, 'upload'))->toBe($mockResponse);
+        });
+
         it('forwards multiple files uploaded under the same field name without crashing', function () {
             $file1 = UploadedFile::fake()->create('one.txt', 5, 'text/plain');
             $file2 = UploadedFile::fake()->create('two.txt', 5, 'text/plain');